Solar batteries have been recognized as important as clean energy sources, and as such, have been in increasing demand. Solar batteries are used in a wide range of fields from power energy sources for large machinery to small-sized power sources for precision electronics. In order for solar batteries to be widely used in a variety of fields, it is necessary that the characteristics, in particular output characteristics, of the solar batteries be accurately measured. Unless the output characteristics are not accurately measured, there will be various inconveniences on the side of solar-battery users. Under such circumstances, there is a particular demand for a technology which can be used for inspections of, measurements of, and experiments on solar batteries and which can irradiate a large area with high-precision simulated sunlight.
Accordingly, a simulated sunlight irradiation apparatus has recently been under development as an apparatus that can radiate simulated sunlight. In general, the simulated sunlight irradiation apparatus is used for measuring the output characteristics of a panel-shaped solar battery by irradiating a receiving surface of the solar battery with artificial light (simulated sunlight) of uniform illuminance.
A major requirement for simulated sunlight is getting closer in emission spectrum to reference sunlight (as defined by the Japanese Industrial Standards: JIS C8941). In other words, the simulated sunlight irradiation apparatus is required, in particular, to be high in spectral coincidence. The term “spectral coincidence” here means the proximity of simulated sunlight in spectrum to the reference sunlight. However, the simulated sunlight irradiation apparatus is only provided with light source lamps in the form of dots or lines (dot-like light sources or linear light sources). This problematically makes it extremely difficult to irradiate the whole (or entire) receiving surface, which is in the form of a plane, of a solar battery with simulated sunlight of uniform illuminance.
In order to solve this problem, Patent Literatures 1 and 2 each disclose a technology for correcting nonuniformity in illuminance of a simulated sunlight irradiation apparatus.
Patent Literature 1 discloses a simulated sunlight irradiation apparatus (solar simulator) having a halogen lamp and a xenon lamp provided in separate chambers adjacent to each other. Specifically, the simulated sunlight irradiation apparatus has a dedicated optical filter provided in an open section above each of the lamps. This causes the receiving surface of a solar battery to be irradiated with simulated sunlight due to lighting of the lamps below. Furthermore, the simulated sunlight irradiation apparatus has a reflective plate in each of the chambers in which the respective lamps are provided. This makes it possible to correct nonuniformity in illuminance among the lamps.
Meanwhile, Patent Literature 2 discloses a simulated sunlight irradiation apparatus (solar simulator) that has a light intensity adjustment member provided for each of those zones into which the receiving surface of a solar battery is imaginarily divided. Specifically, the simulated sunlight irradiation apparatus has three types of light intensity adjustment member having different light-blocking rates. The light intensity adjustment members have their light-blocking rates set so that with reference to the illuminance of the darkest zone of the receiving surface of a solar battery, the illuminances of the other zones are made the same as the illuminance of the darkest zone. This makes it possible to make the illuminance of the light sources in one zone of the receiving surface substantially the same as that in another zone of the receiving surface.